refactor: Print verbose serialize compiler error messages

maflcko commented at 9:21 pm on December 11, 2023: member

Currently, trying to serialize an object that can’t be serialized will fail with a short error message. For example, the diff and the error message:

 0diff --git a/src/test/serialize_tests.cpp b/src/test/serialize_tests.cpp
 1index d75eb499b4..773f49845b 100644
 2--- a/src/test/serialize_tests.cpp
 3+++ b/src/test/serialize_tests.cpp
 4@@ -62,6 +62,8 @@ public:
 5 
 6 BOOST_AUTO_TEST_CASE(sizes)
 7 {
 8+    int b[4];
 9+    DataStream{} << b << Span{b};
10     BOOST_CHECK_EQUAL(sizeof(unsigned char), GetSerializeSize((unsigned char)0));
11     BOOST_CHECK_EQUAL(sizeof(int8_t), GetSerializeSize(int8_t(0)));
12     BOOST_CHECK_EQUAL(sizeof(uint8_t), GetSerializeSize(uint8_t(0)));

0./serialize.h:765:6: error: member reference base type 'const int[4]' is not a structure or union
1  765 |     a.Serialize(os);
2      |     ~^~~~~~~~~~

0./serialize.h:277:109: error: no matching function for call to 'UCharCast'
1  277 | template <typename Stream, typename B> void Serialize(Stream& s, Span<B> span) { (void)/* force byte-type */UCharCast(span.data()); s.write(AsBytes(span)); }
2      |                                                                                                             ^~~~~~~~~

This is fine. However, it would be more helpful for developers and more accurate by the compiler to explain why each function is not selected.

Fix this by using C++20 concepts where appropriate.

DrahtBot commented at 9:21 pm on December 11, 2023: contributor

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Type	Reviewers
ACK	TheCharlatan, ajtowns, achow101
Concept ACK	ismaelsadeeq

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DrahtBot renamed this:
~~refactor: Print verbose serialize compiler error messages~~
refactor: Print verbose serialize compiler error messages
on Dec 11, 2023

DrahtBot added the label Refactoring on Dec 11, 2023

maflcko force-pushed on Dec 11, 2023

in src/span.h:294 in fad89dadd2 outdated

290@@ -290,6 +291,7 @@ inline unsigned char* UCharCast(std::byte* c) { return reinterpret_cast<unsigned
291 inline const unsigned char* UCharCast(const char* c) { return reinterpret_cast<const unsigned char*>(c); }
292 inline const unsigned char* UCharCast(const unsigned char* c) { return c; }
293 inline const unsigned char* UCharCast(const std::byte* c) { return reinterpret_cast<const unsigned char*>(c); }
294+static_assert(std::is_same_v<unsigned char, uint8_t>); // This codebase assumes that uint8_t exists and is equal to unsigned char

TheCharlatan commented at 1:22 pm on December 12, 2023:

Nit: Should this rather be in assumptions.h if it counts for the entire codebase?

maflcko commented at 2:45 pm on December 12, 2023:

Yes, but I guess it is not too useful, so I’ve dropped the commit for now.

TheCharlatan approved

TheCharlatan commented at 2:32 pm on December 12, 2023: contributor

concept ACK fa180c523a173550ab4e549788cb21d4e7994118 :tada:

This:

0./serialize.h:763:6: note: candidate template ignored: constraints not satisfied [with Stream = DataStream, T = Span<int>]
1void Serialize(Stream& os, const T& a)
2     ^
3./serialize.h:762:14: note: because 'Serializable<Span<int>, DataStream>' evaluated to false
4    requires Serializable<T, Stream>
5             ^
6./serialize.h:760:52: note: because 'a.Serialize(s)' would be invalid: no member named 'Serialize' in 'Span<int>'
7concept Serializable = requires(T a, Stream s) { a.Serialize(s); };
8                                                   ^
91 error generated.

is definitely more understandable than

0./serialize.h:765:6: error: member reference base type 'const int[4]' is not a structure or union
1    a.Serialize(os);
2    ~^~~~~~~~~~

maflcko force-pushed on Dec 12, 2023

fanquake requested review from ryanofsky on Dec 12, 2023

TheCharlatan approved

TheCharlatan commented at 3:49 pm on December 12, 2023: contributor

Re-ACK fa45567e030272d34845e6b563a6b626b9eda739

ismaelsadeeq commented at 12:00 pm on December 14, 2023: member

Concept ACK

in src/span.h:296 in fa45567e03 outdated

292 inline const unsigned char* UCharCast(const char* c) { return reinterpret_cast<const unsigned char*>(c); }
293 inline const unsigned char* UCharCast(const unsigned char* c) { return c; }
294 inline const unsigned char* UCharCast(const std::byte* c) { return reinterpret_cast<const unsigned char*>(c); }
295+// Helper concept for the basic byte type.
296+template <typename B>
297+concept BasicByte = requires { UCharCast(std::span<B>{}.data()); };

ajtowns commented at 1:53 am on December 15, 2023:

Perhaps describe it as “Helper concept for basic byte types” ? “BasicByte” is a concept that applies to types, not a type itself? Could name the concept as BasicByteType since it applies to types?

Consider adding .clang-format fields:

0BreakBeforeConceptDeclarations: Always
1RequiresExpressionIndentation: OuterScope

maflcko commented at 2:20 pm on December 15, 2023:

Thanks,

added “s”
Left it as BasicByte for now, to mirror the stdlib naming: https://en.cppreference.com/w/cpp/concepts/floating_point
Added clang-format fields

in src/serialize.h:760 in fa45567e03 outdated

758  * If none of the specialized versions above matched, default to calling member function.
759  */
760-template<typename Stream, typename T>
761-inline void Serialize(Stream& os, const T& a)
762+template <class T, class Stream>
763+concept Serializable = requires(T a, Stream s) { a.Serialize(s); };

ajtowns commented at 2:18 am on December 15, 2023:

Could consider:

 0template <class Stream>
 1concept WritableStream = requires(Stream& s, const Span<std::byte> src) { s.write(src); };
 2
 3template <class T, class Stream>
 4concept Serializable = WritableStream<Stream> && requires(T a, Stream s) { a.Serialize(s); };
 5
 6template <class Stream>
 7concept ReadableStream = requires(Stream& s, Span<std::byte> dst) { s.read(dst); };
 8
 9template <class T, class Stream>
10concept Unserializable = ReadableStream<Stream> && requires(T a, Stream s) { a.Unserialize(s); };

maflcko commented at 2:20 pm on December 15, 2023:

Shouldn’t WritableStream be applied at all implementations instead to constrain them? Otherwise, one could still call Object{}.Serialize(WrongStream{}) in other parts of the code?

ajtowns commented at 3:26 pm on December 15, 2023:

Yeah, that’s probably reasonable

ajtowns commented at 4:23 am on December 15, 2023: contributor

utACK fa45567e030272d34845e6b563a6b626b9eda739

DrahtBot requested review from ismaelsadeeq on Dec 15, 2023

refactor: Print verbose serialize compiler error messages fa898e6836

Allow std::byte C-style array serialization fae526345d

maflcko force-pushed on Dec 15, 2023

maflcko requested review from TheCharlatan on Dec 19, 2023

TheCharlatan approved

TheCharlatan commented at 3:55 pm on December 19, 2023: contributor

Re-ACK fae526345de539ab8f9b80100f6dfbe8e1d3284b

DrahtBot requested review from ajtowns on Dec 19, 2023

ajtowns commented at 5:48 am on December 20, 2023: contributor

reACK fae526345de539ab8f9b80100f6dfbe8e1d3284b

DrahtBot removed review request from ajtowns on Dec 20, 2023

achow101 commented at 5:08 pm on December 21, 2023: member

ACK fae526345de539ab8f9b80100f6dfbe8e1d3284b

achow101 merged this on Dec 21, 2023

achow101 closed this on Dec 21, 2023

maflcko deleted the branch on Dec 22, 2023

calmbeforeu approved

sins921 commented at 8:44 pm on February 9, 2025: none

Gracias

refactor: Print verbose serialize compiler error messages #29056

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